The Impossible Girl
by Booklover291197
Summary: Set after COHF. When a strange silent girl turns up in the New York Institute it will all change...
1. Hell & Silence

**Hia, this is my first attempt at a crossover, but this idea really began to form after I finished reading The Infernal Devices for the second time so I thought I'd give it a shot. Hope you enjoy, please review 3**

Jace was still smiling when he walked down the familiar corridor to his room in the New York Institute. Seeing Clary always put him in a good mood, even the sound of her name gave him butterflies. He pushed open his door and looked into the room, it was as it always was, too clean and yet not ever clean enough. There was just one change, one big change.

There was a girl standing in his room.

Not any ordinary girl ever. This girl was about ten years old, with long wavy black hair and bright clear blue eyes. She was wearing a long black dress, that reminded Jace of something he had seen in a history book to do with Victorian England.

After he realised he had been standing staring at her for a couple of minutes he abruptly cleared his throat and questioned "What are you doing here?" adding as an afterthought "Who are you?"

She did not answer his question, in fact the only thing she done to indicate she had heard him at all was to raise an eyebrow.

Perplexed he tried again "Are you a shadowhunter?"

She continued to stare.

Getting slightly annoyed now he said "You're not meant to be up here if you want to talk to somebody you need to go down stairs."

This time she moved and walked past him out the door. Following her he realise she must have been in an Institute before because she moved with nothing but certainty, which was almost impossible for someone with no experience because Institutes were built purposely like labyrinths.

Eventually they made it to the bottom floor just in time for the front door to open. Clary walked in first, Simon following, both were laughing. The girl stopped in her tracks and froze. Both Clary and Simon stared at the girl, Simon's mouth dropping open.

Clary caught sight of Jace and asked in a slightly higher pitch than normal "Who's this?"

"I have no idea, she doesn't really talk."

"Maybe she doesn't like you" Simon noted unhelpfully.

"Maybe" he said "But that is highly unlikely _everyone_ likes _me_"

Clary rolled her eyes and addressed the girl "Are lost?"

The girl stayed silent. More amounts of people seemed to be agitating her rather than scaring her, which would have been a _normal_ reaction for a young girl surrounded by strangers.

Clary looked at him for help but he just shrugged as confused as her. Simon was just staring trying to figure out whether she was a shadowhunter probably.

The door opened again but this time Alec walked in, it had clearly began to snow outside as his hair was covered in white flakes. He looked up to see why they were all standing in the entrance hall. For the first time to girl reacted, a very small gasp almost inaudible in fact, but because everyone had been watching her so intently the noise might have been a shout.

Alec's eyebrows drew together in confusion, as the Institute door opened one last time to admit Magnus, who was covered in a thick layer of snow.

"Magnus!" at last the girl had broken her silence saying the warlocks name like a prayer.

Magnus looked up and sighed "Well that's not good."


	2. Lost in Translation

**Please review x**

"_Well that's not good."_

"Magnus!" she cried again and ran over putting her arms around the warlocks waist, holding on for dear life.

Every head in the entrance hall snapped around in shock.

"Well this is interesting" Simon put in.

"What's going on?" Alec questioned looking just as confused as everyone else.

"I honestly have no idea" Magus said removing the girl from himself and bending down to her height putting his hands on her shoulders, he said very carefully "Do you know where you are, cupcake?"

She shook her head.

"Ok, well this is going to be a _long _day" standing up he spoke to the room at large "Come on, we may as well sit down"

They walked to the dining room, and sat down.

"Why is it every time we have a group discussion it feels like knights of the round table?" Jace asked in an offhand tone.

Nobody answered so Magnus turned to the girl and said "I think it's time you told everyone who you are, don't you think sweetheart?"

She began to shake her head violently.

"The sooner you tell us, the sooner we know how you got here, the sooner we can figure out how to get you home" he said encouragingly.

She looked down at the table and began in a small voice "My name is Lucie Herondale, I'm ten years old, my mother is Tessa Herondale, my father is William Herondale and my brother is James Herondale, I live in the London Institute"

There was a murmuring around the table but Magus silenced them with a look "What was the date when you left?"

"25th December 1886"

This time the murmuring became louder and louder.

Her small voice managed to cut everyone else "Am I in the New York Institute? That's where mother said you went Magnus."

When Magnus failed to answer Clary Said kindly "Yes, darling"

Lucie didn't look impressed by being addressed as darling by a strange girl, even if that girl had Henry's red hair. The boy who stayed close to Magnus looked remarkably like her father and the sarcastic golden boy defiantly had her brothers eyes. _This is so confusing _she thought.

Seeing her disorientation Alec took pity and said steadily "Do you want to know the date now?"

Her eyebrow drew down but she nodded regardless "Please"

"It's the 1st January 2013"

Her mouth fell open, her eyes going wide "How?!"

Magnus rolled his eyes at his boyfriend and addressed Lucie "I was hoping you could tell us that. Tell me what you were doing before you were here"

Taking a deep breath she started "Well obviously I was at the Christmas party, and James said we should play hide and seek. So I decided to hide in Henry's experiment room –"

She was interrupted by Magnus groaning and she said quickly "I know, I know I'm not supposed to be in there. But I thought it would be the last place James would look. Anyway I saw this weird rune on the wall, kind of like the portal rune but different like the one mother makes, you know?"

Most heads turned to Clary as she said "Make runes? Your mother can make runes too?"

"Too?" Lucie said puzzled.

Magnus raised a hand to stop Clary replying "We can get to that later, please continue"

"Um…well I touched it" then with a touch of panic "I don't know why I just did and then the portal materialised and pulled me in, but when I came out the other side nothing looked _very_ different, apart from the fact I came out into my room you see, but it was not quite my room at the same time and then _he_ walked in" she said indicating Jace.

"Well it is _my_ room" Jace said brazenly.

"Not really , nobody really _owns_ anything in an Institute as it is owned by the Clave, we are just it's keepers" Alec added unnecessarily.

Both Lucie and Jace rolled their eyes at the same time, making everyone stare.

"Let me see your hands"

Lucie presented her hands to Magnus palms up. Everyone leaned in to see that her palms had been scrapped up, dried blood congealed there.

"Ah" Magnus said as softly if this explained everything.

"I fell on the way down the stairs to the experiment room" she said defensively.

"That would explain it"

"Well I'm glad that's all sorted, now we all understand what happened, yay!" Simon said happily.

Alec gave him a disgusted look and turned to Magnus "What's happened?"

"Well" the warlock said in an animated voice "It seems that the rune Tessa created was dormant in the lab, but when Lucie's unique mixture of shadowhunter and warlock blood touched it, it reacted and woke up the power within the rune"

Ignoring the shadowhunter and warlock blood mixture comment Jace asked "What do we do now?"

"Lucie could you take us to where you can through?"

"Certainly" she said politely.

They all followed the small girl up to Jace's room when she flung open the wardrobe doors, and there was the portal.

"You never told us you had the way to Narnia" Simon said to Jace.

Clary elbowed him painfully in the ribs, and Jace laughed. The noise was cut off abruptly as the portal began to pulse.

"Someone's coming through" Alec said to no one in particular, as they all stood waiting for their next guest to come through.


	3. The Clash of Blue

**Hey guys, sorry this one took a while I've been really busy. Hope you enjoy ;) Please review x**

"Someone's coming through" Alec said to no one in particular, as they all stood waiting for their next guest to come through.

The portal began to pulse again, but this time it separated to emit the next visitor.

William Herondale looked up into the many astounded face that were turned to him. He caught the familiar slit pupil eyes, asking them a silent question, to which Magnus nodded down to Lucie.

Spotting her father, the girl in question ran forward and began to sob, in fluent welsh "Mae'n ddrwg gen i, felly mor flin. Doeddwn i ddim yn ei olygu i ei fod yn damwain! Peidiwch â bod yn ddig gyda mi thad."

Replying to her in English, Will said soothingly, whilst stroking her hair "Of course it was an accident." however his voice still took on a sterner tone "But you knew better than to be down there."

Lucie nodded feverishly, wiping away her tears with one arm. Looking again into the crowd Will found his eyes lingering on one boy who looked suspiciously like he had the same shade of blue eyes as himself, and yet another one with the golden eyes he had come to associate with his son.

Drawing his eyes away he spoke to Magnus "Where are we?"

Sighing Magus replied impatiently "Earth, The United States of America, New York, Brooklyn, The Institute, A bedroom which apparently is not owned by anyone but is kept nice for the Clave anyway"

Alec mumbled something that sounded like 'well it is' and Magnus shot him a look.

Waving a hand carelessly he added "Oh, and it's the 1st January 2013, because that's also quite important apparently"

Will blinked at him once and shrugged "Fair enough"

When no one else spoke the warlock said bracingly "Come on my little sheep, we may as well do introductions down stairs, doesn't look like this is going to be solved any time soon we might as well try and be comfortable"

With that they all went downstairs and back into dining room. Lucie sat on her father's lap huddled up as if she feared he would vanish in the blink of an eye.

"It's amazing how all Institutes are so similar" Will commented, earning a disbelieving look from Magnus.

"What?" he asked

"Nothing" replied the warlock sounding tired.

"Ok…so, if you haven't all guessed it by now this is William (Will) Owen Herondale"

Will raised a hand in acknowledgment, even if he did look slightly confused at how Magnus knew his middle name.

"Ok, pay attention this is going to be a slightly longer list" after checking to see that Will was indeed paying full attention, Magus called out the names of each person in turn, pointing to make sure it was clear "Clarissa (Clary) Adele Fairchild, Alexander (Alec) Gideon Lightwood, Sydney Lewis and Johnathan (Jace) Christopher Herondale"

"Simon!" Simon added irritably as Jace snickered.

Will had given a range of expressions as he had heard the names. He had rolled his eyes at Alec's name and made a noise of someone finally finding out the answer to a particularly difficult puzzle when Jace was revealed as a Herondale.

He was excused from making a comment however as at that very moment the dining room door was flung open and a tall girl, with long black hair and equally black eyes barged in.

"There is a women saying she wants to see Magnus Bane, she said her name is Tessa Gray" Isabelle said not quite taking in the tense atmosphere of the room.

Will gave a start and made to get up, but was impaired by his daughter being on his lap. Taking the opportunity whilst it lasted, Magnus sprang out of the chair and through the open door locking it firmly behind him…

_For those who are wondering here is the translation for what Lucie says earlier : "I'm sorry, so so sorry. I didn't mean to do it! Please don't be angry with me father."_


	4. Begin Again

**This one is kind of sad :/ I'd like to thank Crazycuz for being a beta for this chapter ****J Please review x**

_Taking the opportunity whilst it lasted, Magnus sprang out of the chair and through the open door, locking it firmly behind him…_

Magnus ran out the front doors of the Institute just in time to see a young woman with dark, flowing brown hair and wild grey eyes climbing the stone steps. She was bare-footed and was dressed in ripped jeans and a thin white shirt. The temperature was well below freezing on this particularly snowy New York winter night but she did not have a jacket, as if she had forgotten it in the rush to get here.

She looked up at Magnus, frantically saying, "I felt it, Magnus! I was just reading and then my memories suddenly started to blur and change! And by the Angel, Magnus, they're still changing!"

Tessa tried to push her way into the place that held all the last traces of her family, but Magnus held her steady.

"No," he said gently. "It's not worth it."

_"'NOT WORTH IT'?!" _she screeched so loudly that Magnus was sure that the entire street was able to hear her.

Realising he had indeed been slightly brash with his words, Magnus rested a hand on either side of her head, which was somewhat difficult to do considering that she was fighting tooth and nail to get inside the building, and said sternly, "You _know _what I meant."

She continued to struggle but Magnus would not move a single inch. Realising that she would not be able to get past someone much stronger than herself, Tessa felt a sense of hopelessness crash over her. Finally, her legs gave way and she began to sob hysterically.

Crouching down, Magnus took off his extravagant fur coat and wrapped it around her shoulders.

It was then that he heard the sound of approaching footsteps and looked up. The warlock was faced with the figure of a young man standing above them. The look on the Eurasian man's face was one of such overwhelming sadness that Magnus felt his own heart ache.

"Jem," Magnus acknowledged, hoping that his arrival would get the sobbing girl's attention. However, it did not and she just continued to cry convulsively.

"Is it true?" Jem said quietly, his voice almost an inaudible whisper, bending down to wrap an arm around Tessa.

"Yes," Magnus confirmed, feeling like a doctor telling someone that they had contracted a terminal illness.

Jem raised a shaky hand to his _parabatai _rune and took a shuddering breath before putting his lips to her ear and whispering, "Tessa my love, _wǒ qīn aì de rén,_ you can mourn however you want for however long you want afterward, but we need to set things right first, do you understand? You don't want those memories to be gone forever, do you Tessa?"

Tessa's crying began to dull to a whimper but her breathing was still erratic as she shook her head.

"Then once again we must be the ones who remain strong."

"But they are my family…" she protested, her voice hoarse.

"You will _always _have family," Jem said while looking up at Magnus.

"Always," the cat-eyed warlock said simply, then added, "Tessa sweetheart, you barely made it through losing him the first time, we all know you will not survive having to do it again."

Upon hearing that, Tessa let out one final single sob.

* * *

><p>Inside the Institute Will stood, head leaning against the door with one hand pressed up against it. Hearing each one of her desperate sobs made him feel as if knives were embedding themselves one after another in his gut.<p>

He knew exactly why Magnus had to keep them apart. It was for her sake. But knowing that did not really make the facts any less painful.

If it really _was _2013 then he was most definitely dead and had been for many years now. Once, he had even been sure that any grandchildren, if they ever had any, would also be dead. However, that assumption had been proven wrong by the golden boy sitting in the same room he was in who wouldn't have existed otherwise.

A sudden thought that occurred to him made him feel like bucket upon bucket of ice had been poured over his head. Jem_. _Was he still a silent brother? Had they found a cure at last? Will frowned. Or was he _gone_? No, he couldn't be. An odd tingling sensation in his faded _parabatai _rune told him Jem was still very much alive.

Will felt a tug on the back of his coat and looked down. Lucie had gone back to her customary silence, but the fear in her eyes made him realise that they had to leave sooner rather than later. And it had to be while he still had the strength to keep himself from knocking down the very door he was leaning on, no matter the cost.

The redheaded girl in the corner, _Clary, _he thought her name was, walked over to the wall next to where he stood and drew out her _stele. _Before Will could ask her what she was doing she began to draw a rune on the surface. A rune that he had never seen before in his entire life. The only reason he did not freak out was because he had first-hand experience of watching a person create runes no one else could.

When she was finished, she turned and asked Lucie gently, "Does that look like the rune you saw before?"

Lucie nodded affirmatively in delight.

The golden boy in the corner - alright, maybe he _should _start calling him by his name - stood up and asked Clary, "How did you know that?"

She shrugged while smirking at him as he gazed down in wonderment at her before shaking his head. "Clary Fray, you never cease to amaze me."

Just when he was _very _tempted to join in the flirting fest, the doors of the Institute opened and Will found himself face to face to a young male no older than himself, with brown hair and eyes that were both so dark that they could be mistaken as black. However, the most outstanding feature about him was the strip of silver in his hair that stood out against the darkness. He looked almost... familiar...

_Who was he?_

Clary perked up. "Brother-"

It was then recognition hit him like a sledgehammer. He heard his own voice murmur dazedly, "_Jem._"


End file.
